The present invention relates to a method and device at a single chamber air drier in a compressed air system for determining the volume of dry regeneration air required to regenerate a desiccant in the air drier.
A compressed air system for a vehicle, normally a truck or bus, usually includes an air drier for removing moisture from the air, as the moisture can be detrimental for air consumers in the vehicle, such as brakes, air suspensions, and door openers.
The supplied volume of air in the compressed air system varies depending on the driving conditions and the vehicle type.
Climate conditions also vary considerably and thus the moisture content of the air, which directly influences the air drier.
Further, the compressed air is often contaminated in the compressor by its lubricant, which partly joins the air flow into the compressed air system and gradually deteriorates the desiccant in the air drier.
The conventional way to regenerate the desiccant in a single chamber air drier is to supply a constant volume of dried air from the system, either via a special regeneration tank or via a regeneration valve opening for a fixed time period.
This method implies that the volume of regeneration air has to be over-dimensioned in order to manage the few worst loads on the desiccant with regard to throughput air volume and the moisture content of the air.
The contamination of the desiccant gradually decreases the capacity, so that the drying effect gradually disappears in spite of sufficient regeneration capacity.
The Invention
In a method according to the invention the determination of the required volume of dry regeneration air is achieved in that data regarding system pressure, outdoor temperature and supplied air volume are continuously provided to a computer, which in relation to these parameters controls the supply of regeneration air to the air drier.
A device for carrying out this method has a computer for controlling two solenoids at the air drier, wherein the first solenoid provides a pilot signal to an unloader valve of the air drier and the second solenoidxe2x80x94subordinated to the first solenoid valvexe2x80x94controls the volume of regeneration air supplied to the air drier and wherein the computer is arranged to continuously receive data regarding system pressure, outdoor temperature and supplied air volume.
By substituting the conventional mechanical/pneumatical valves in the air drier and sometimes the regeneration tank for two solenoid valves controlled via an onboard computer, a variable volume of regeneration air can be produced and the influence on the drying function of the system pressure, the temperature, and contaminations can be taken into account for the purpose of making the use of the regeneration air more effective, which leads to an improved drying function, energy saving, lower maintenance, and lower installation costs.
If the air drier has a large capacity, the new control makes it possible to determine the conditions for optimizing the use of the vehicle. This means that the calculated need for regeneration air can be stored in a memory, so that the balance in the air drier can be restored at a suitable time. The normal pressure span can be varied for varying the number of drainages and regenerations, and the wear of the desiccant can be taken into account.
A diagnosis system can also be provided, which gives information when a serious system failure occurs or when the compressed air consumption goes outside limits where dry air can be guaranteed.